Inflatable restraint systems, commonly referred to as airbag systems, which deploy automatically in the event of a collision to shield and cushion the occupants of a vehicle from the hard surfaces within the passenger compartment, have become very popular in modern motor vehicles. Many types of inflator devices for inflating the airbag cushion in such systems have been disclosed. Such inflators should be capable of releasing a sufficient quantity of a non-toxic gas to inflate the airbag cushion in a very short period of time. Additionally, the inflator needs to provide a high degree of reliability over the extended temperature range in which modern vehicles are expected to operate, and over the extended lifetime of the vehicle.
One of the disclosed inflator designs relies on a stored compressed gas which is released to inflate the airbag. Another design relies on the ignition of a solid gas generating material to produce a sufficient quantity of gas to inflate the airbag. A third type of inflator relies on the combination of an inert stored compressed gas and the combustion of a solid gas generating material. While these designs are functional to provide the gas needed to inflate an airbag, they each have disadvantages. The designs which rely solely on compressed gas must provide a strong gas storage container, the relatively thick walls of which increase the weight and bulk of the airbag assembly, a concern to those vehicle manufacturers who seek to minimize the weight of such vehicles. The designs which rely on the ignition of a gas generant material often result in a generated gas which contains solid particulate material at an elevated temperature, requiring that the gas be further conditioned, by filtration and cooling, before it encounters the fabric cushion of the airbag assembly.
Some of the more recent inflator designs rely on fluid fuels and oxidants which, in addition to lower manufacturing costs, offer advantages such as cleaner generated gases containing little or no solid particulate matter, and which can be provided at relatively low temperatures and with relatively low concentrations of products of incomplete combustion. Some of these designs are more fully described in U.S. patent application Ser. No. 08/252,036, entitled FLUID FUELED AIR BAG INFLATOR, filed on May 31, 1994 by Bradley W. Smith and Karl K. Rink, now U.S. Pat. No. 5,470,104 and commonly assigned with this application. Application Ser. No. 08/252,036 is hereby incorporated by reference herein.
A need exists, however, to improve the design of the known liquid fueled inflators to provide structural characteristics which provide regulation of the gas storage, heating and release procedure whereby the proper design of the structure enables the inflation characteristics of the airbag to be tailored to meet specific requirements. Some of the liquid fuels result in a high rate of gas delivery which could cause excessive stress on the airbag cushion and module. Such fuels further raise concern about possible injury to an out-of-position occupant. The capability of tailoring the gas delivery rate, through the selection of structural parameters of the components of the airbag system, provides flexibility in the selection of different fuels to be used in such systems. The designs must also provide for the flammable components to be held safely over the expected lifetime of the vehicle. Further, the designs need to reliably produce an inflation gas which does not contain significant amounts of relatively toxic incompletely combusted gases. Finally, the designs should be able to be manufactured and filled with the flammable mixtures quickly and safely.